Wireless communication terminal and wireless communication method for random access-based uplink multi-user transmission

ABSTRACT

Provided are a wireless communication terminal including: a processor; and a communication unit, wherein the processor obtains a backoff counter for an OFDMA-based random access of the terminal, wherein the backoff counter is obtained within a range of a contention window for the uplink OFDMA-based random access, receives a trigger frame indicating an uplink multi-user transmission, when one or more resource unit(s) in which random access can be performed is indicated by the trigger frame, decrements the backoff counter based on a number of resource units(s) in which random access can be performed, and when the backoff counter is 0 or decremented to 0, performs an uplink multi-user transmission through a selected resource unit among the resource units(s) and a wireless communication method using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/188,274 filed on Nov. 12, 2018, which is a continuation ofInternational Patent Application No. PCT/KR2017/004889 filed on May 11,2017, which claims the priority to Korean Patent Application No.10-2016-0057759 filed in the Korean Intellectual Property Office on May11, 2016, Korean Patent Application No. 10-2016-0117898 filed in theKorean Intellectual Property Office on Sep. 13, 2016, and Korean PatentApplication No. 10-2017-0002720 filed in the Korean IntellectualProperty Office on Jan. 9, 2017, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication terminal and awireless communication method for an uplink multi-user transmissionbased on random access, and more particularly, to a wirelesscommunication terminal and a wireless communication method forefficiently performing contention for random access in an uplinkmulti-user transmission.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention has an object to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment as described above.

In addition, the present invention has an object to efficiently manage arandom access procedure of a plurality of terminals.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an exemplary embodiment of the present invention provides awireless communication terminal, including a processor; and acommunication unit, wherein the processor obtains a backoff counter foran uplink multi-user random access of the terminal, wherein the backoffcounter is obtained within a range of a contention window for the uplinkmulti-user random access, receives a trigger frame indicating an uplinkmulti-user transmission, when the trigger frame indicates at least oneresource unit allocated for random access, decrements the backoffcounter based on a number of resource units(s) in which random accesscan be performed in response to the trigger frame, and when the backoffcounter is 0 or decremented to 0, select at least one of resourceunits(s) allocated for the random access, and perform an uplinkmulti-user transmission through the selected resource unit.

In addition, an exemplary embodiment of the present invention provides awireless communication method of a wireless communication terminal,including: obtaining a backoff counter for an uplink multi-user randomaccess of the terminal, wherein the backoff counter is obtained within arange of a contention window for the uplink multi-user random access;receiving a trigger frame indicating an uplink multi-user transmission;when the trigger frame indicates at least one resource unit allocatedfor random access, decrementing the backoff counter based on a number ofresource units(s) in which random access can be performed in response tothe trigger frame, and when the backoff counter is 0 or decremented to0, performing an uplink multi-user transmission through a selectedresource unit among resource units(s) allocated for the random access.

When carrier sensing is required before the uplink multi-usertransmission in response to the trigger frame, the processor performscarrier sensing on a channel containing the selected resource unit, andwhen the channel containing the selected resource unit is determined tobe idle as a result of the carrier sensing, the processor transmituplink multi-user data through the selected resource unit.

When the channel containing the selected resource unit is determined tobe busy as a result of the carrier sensing, the processor does nottransmit uplink multi-user data through the selected resource unit, andrandomly obtains a new backoff counter for an uplink multi-user randomaccess of the terminal within the range of the contention window, andparticipates in a subsequent uplink multi-user random access using theobtained new backoff counter.

The contention window for obtaining the new backoff counter has the samesize as an existing contention window.

The carrier sensing is performed during a SIFS time between the triggerframe and a PHY protocol data unit (PPDU) transmitted in response to thetrigger frame.

The processor decrements the backoff counter if the terminal has pendingdata to be transmitted to a base wireless communication terminal.

A minimum value of the contention window and a maximum value of thecontention window for determining the contention window are transmittedthrough a random access parameter set.

The random access parameter set is included in a beacon and a proberesponse.

The uplink multi-user random access is an uplink OFDMA-based randomaccess.

Advantageous Effects

According to an embodiment of the present invention, a random accessprocedure of a plurality of terminals can be efficiently managed.

According to an embodiment of the present invention, it is possible toreduce the probability of occurrence of a collision by preventing anexcessive accumulation of terminals having a backoff counter of 0 forrandom access.

According to an embodiment of the present invention, it is possible toincrease the total resource utilization rate in the contention-basedchannel access system and improve the performance of the wireless LANsystem.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 illustrates a configuration of a station according to anembodiment of the present invention.

FIG. 4 illustrates a configuration of an access point according to anembodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA and an AP seta link.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

FIG. 7 illustrates an embodiment of an operation of an uplinktransmission terminal in an uplink multi-user transmission process.

FIG. 8 illustrates an embodiment of a subsequent operation of the uplinktransmission terminal when the uplink multi-user transmission hasfailed.

FIG. 9 illustrates another embodiment of a subsequent operation of theuplink transmission terminal when the uplink multi-user transmission hasfailed.

FIG. 10 illustrates yet another embodiment of a subsequent operation ofthe uplink transmission terminal when the uplink multi-user transmissionhas failed.

FIG. 11 illustrates an embodiment of a UL OFDMA-based random accessprocedure.

FIGS. 12 to 15 illustrate embodiments of a UL OFDMA-based random accessprocedure when a carrier sensing is required before the transmission ofa trigger-based PPDU.

FIGS. 16 to 18 illustrate embodiments of an OBO counter managementmethod of a STA that has succeeded in a UL OFDMA-based random access.

FIGS. 19 and 20 illustrate embodiments of a UL OFDMA-based random accessprocedure when a STA does not have pending data to be transmitted.

FIGS. 21 and 22 illustrate protection methods of the UL OFDMA-basedrandom access procedure.

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2016-10057759, 10-2016-0117898 and 10-2017-0002720filed in the Korean Intellectual Property Office and the embodiments andmentioned items described in the respective application, which forms thebasis of the priority, shall be included in the Detailed Description ofthe present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a communication unit andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the communication unit is functionallyconnected with the processor and transmits and receives frames throughthe wireless network for the station. According to the presentinvention, a terminal may be used as a term which includes userequipment (UE).

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense. In the present invention, an AP may also be referredto as a base wireless communication terminal. The base wirelesscommunication terminal may be used as a term which includes an AP, abase station, an eNB (i.e. eNodeB) and a transmission point (TP) in abroad sense. In addition, the base wireless communication terminal mayinclude various types of wireless communication terminals that allocatemedium resources and perform scheduling in communication with aplurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention. As illustrated inFIG. 3, the station 100 according to the embodiment of the presentinvention may include a processor 110, a communication unit 120, a userinterface unit 140, a display unit 150, and a memory 160.

First, the communication unit 120 transmits and receives a wirelesssignal such as a wireless LAN packet, or the like and may be embedded inthe station 100 or provided as an exterior. According to the embodiment,the communication unit 120 may include at least one communication moduleusing different frequency bands. For example, the communication unit 120may include communication modules having different frequency bands suchas 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station100 may include a communication module using a frequency band of 6 GHzor more and a communication module using a frequency band of 6 GHz orless. The respective communication modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingcommunication module. The communication unit 120 may operate only onecommunication module at a time or simultaneously operate multiplecommunication modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of communication modules, each communication module may beimplemented by independent elements or a plurality of modules may beintegrated into one chip. In an embodiment of the present invention, thecommunication unit 120 may represent a radio frequency (RF)communication module for processing an RF signal.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the communication unit120, and the like. That is, the processor 110 may be a modem or amodulator/demodulator for modulating and demodulating wireless signalstransmitted to and received from the communication unit 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the communication unit 120 may be implemented whilebeing integrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention. As illustrated inFIG. 4, the AP 200 according to the embodiment of the present inventionmay include a processor 210, a communication unit 220, and a memory 260.In FIG. 4, among the components of the AP 200, duplicative descriptionof parts which are the same as or correspond to the components of thestation 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the communication unit 220 for operating the BSS in at leastone frequency band. As described in the embodiment of FIG. 3, thecommunication unit 220 of the AP 200 may also include a plurality ofcommunication modules using different frequency bands. That is, the AP200 according to the embodiment of the present invention may include twoor more communication modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a communication module using a frequency band of 6 GHz or moreand a communication module using a frequency band of 6 GHz or less. Therespective communication modules may perform wireless communication withthe station according to a wireless LAN standard of a frequency bandsupported by the corresponding communication module. The communicationunit 220 may operate only one communication module at a time orsimultaneously operate multiple communication modules together accordingto the performance and requirements of the AP 200. In an embodiment ofthe present invention, the communication unit 220 may represent a radiofrequency (RF) communication module for processing an RF signal.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. According to an embodiment, the processor210 may be a modem or a modulator/demodulator for modulating anddemodulating wireless signals transmitted to and received from thecommunication unit 220. The processor 210 controls various operationssuch as wireless signal transmission/reception of the AP 200 accordingto the embodiment of the present invention. A detailed embodimentthereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b). In this specification, an association basically means awireless association, but the present invention is not limited thereto,and the association may include both the wireless association and awired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an inter framespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber, that is, a backoff counter determined by the correspondingterminal during an interval of an idle state of the channel and aterminal that completely exhausts the slot time(s) attempts to accessthe corresponding channel. As such, an interval in which each terminalperforms the backoff procedure is referred to as a contention windowinterval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers (i.e. backoff counters), respectively to perform thebackoff procedure again. According to an embodiment, a random numbernewly assigned to each terminal may be decided within a range (2*CW)which is twice larger than a range (a contention window, CW) of a randomnumber which the corresponding terminal has previously used. Meanwhile,each terminal attempts the access by performing the backoff procedureagain in a next contention window interval and in this case, eachterminal performs the backoff procedure from slot time(s) which remainedin the previous contention window interval. By such a method, therespective terminals that perform the wireless LAN communication mayavoid a mutual collision for a specific channel.

Multi-User Transmission

When using orthogonal frequency division multiple access (OFDMA) ormulti-input multi-output (MIMO), a wireless communication terminal cansimultaneously transmit data to a plurality of wireless communicationterminals. Further, a plurality of wireless communication terminals cansimultaneously transmit data to a wireless communication terminal. Forexample, a downlink multi-user (DL-MU) transmission in which an APsimultaneously transmits data to a plurality of STAs, and an uplinkmulti-user (UL-MU) transmission in which a plurality of STAssimultaneously transmit data to the AP may be performed.

In order to perform the UL-MU transmission, a resource unit to be usedby each STA and the transmission start time of each STA that performsuplink transmission should be determined. According to an embodiment ofthe present invention, the UL-MU transmission process may be managed bythe AP. The UL-MU transmission may be performed in response to a triggerframe transmitted by the AP. The trigger frame indicates a UL-MUtransmission a SIFS time after the PHY protocol data unit (PPDU)carrying the trigger frame. Further, the trigger frame delivers resourceunit allocation information for the UL-MU transmission. When the APtransmits a trigger frame, a plurality of STAs transmit uplink datathrough each allocated resource unit at the time specified by thetrigger frame. A UL-MU transmission in response to the trigger frame isperformed by a trigger-based PPDU. After the uplink data transmission iscompleted, the AP transmits an ACK to STAs that have successfullytransmitted uplink data. In this case, the AP may transmit apredetermined multi-STA block ACK (M-BA) as an ACK for a plurality ofSTAs.

In the non-legacy wireless LAN system, a specific number, for example,26, 52, or 106 tones may be used as a resource unit for asubchannel-based access in a channel of 20 MHz band. Accordingly, thetrigger frame may indicate identification information of each STAparticipating in the UL-MU transmission and information of the allocatedresource unit. The identification information of the STA includes atleast one of an association ID (AID), a partial AID, and a MAC addressof the STA. Further, the information of the resource unit includes thesize and placement information of the resource unit.

FIG. 7 illustrates an embodiment of an operation of an uplinktransmission terminal in an uplink multi-user transmission process. Asdescribed above, resource units are allocated to the STAs participatingin the UL-MU transmission through the trigger frame 310, and the STAsreceive MAC protocol data unit (MPDU) or aggregate MPDU (A-MPDU) throughthe allocated resource unit. In this case, the STA transmits (A-)MPDU320 by configuring it according to the transmission length specified inthe trigger frame 310.

The STA participating in the UL-MU transmission may configure the (A-)MPDU 320 based on information of enhanced distributed channel access(EDCA) buffer of the corresponding terminal at the time of receiving thetrigger frame 310. More specifically, the STA determines priority amongthe access categories at the channel access time of the UL-MUtransmission, taking into account a backoff counter and an AIFSN valueremaining for each access category in the EDCA buffer. The (A-) MPDU 320to be transmitted by the STA may first be configured with data of anaccess category of the determined highest priority. Next, the (A-)MPDU320 may be configured to include data of the next priority accesscategory within the allowed transmission length of the STA. Referring toFIG. 7, the priority among the access categories in the EDCA buffer ofSTA1 participating in the UL-MU transmission are determined in the orderof video (VI), voice (VO), background (BK) and best effort (BE). Thus,STA1 configures the (A-)MPDU 320 with data of the highest priority, thatis, VI access category. In addition, STA1 may fill the remaining lengthwithin the allowed transmission length of the (A-)MPDU 320 with data ofVO and BK categories which are the next priorities.

According to an embodiment of the present invention, the STA hastransmitted a buffer status report (BSR) to the AP before the triggerframe 310 is transmitted, and the STA may configure the (A-)MPDU withthe corresponding traffic as the highest priority if the target trafficof the BSR remains in the EDCA buffer. If an allowed transmission lengthof the STA remains, the STA may configure the remaining portion of the(A-)MPDU based on the priority among the above-described accesscategories.

FIG. 8 illustrates an embodiment of a subsequent operation of the uplinktransmission terminal when the uplink multi-user transmission hasfailed. In the contention-based channel access procedure, each terminaluses and manages a backoff counter as in the embodiment of FIG. 6 for asingle-user transmission. However, when participating in thetrigger-based UL-MU transmission, the STA may perform an UL-MUtransmission irrespective of the backoff counter managed by thecorresponding STA. If the STA succeeds in the UL-MU transmission, theSTA may initialize the backoff counter and the retry counter. Ifsubsequent data is present in the queue of the same access category, theSTA may participate in a channel contention by allocating a new backoffcounter for the subsequent data.

However, if the UL-MU transmission of the STA has failed, the STA mayresume the transmission process of the data. According to the embodimentof the present invention, when a response corresponding to thetrigger-based PPDU transmitted by the STA is not received, it can bedetermined that the UL-MU transmission of the STA has failed. The STAmay transmit data that has failed to be transmitted in the UL-MUtransmission process through the subsequent UL-MU transmission processor a single-user transmission process of the corresponding STA.According to the embodiment of FIG. 8, when the data that has failed tobe transmitted in the UL-MU transmission process is transmitted througha single-user transmission process of the corresponding STA, the STAperforms a channel access using an existing backoff counter for asingle-user transmission. The existing backoff counter for a single-usertransmission is a backoff counter maintained by the STA before thecorresponding UL-MU transmission process. That is, if the UL-MUtransmission has failed, the STA may attempt to access the channel byreusing the backoff counter which was maintained for a single-usertransmission.

More specifically, FIG. 8 shows a process in which STA1, which hasfailed in the UL-MU transmission, retries the data transmission througha single-user transmission. In the embodiments of FIG. 8 and thefollowing figures, x and y of <x, y> represent the remaining backoffcounter and the retry counter of the corresponding terminal. Beforereceiving the trigger frame for the UL-MU transmission procedure, theremaining backoff counter of STA1 was 3. STA1 transmits a trigger-basedPPDU in the UL-MU transmission process, but does not receive thecorresponding response. Therefore, STA1 may retry the transmission ofthe corresponding data through a single-user transmission process. Inthis case, STA1 may attempt to access the channel for a single-usertransmission by using the remaining backoff counter 3. If the backoffcounter expires in a subsequent backoff procedure, STA1 may perform thesingle-user transmission.

FIG. 9 illustrates another embodiment of a subsequent operation of theuplink transmission terminal when the uplink multi-user transmission hasfailed. If the STA which has failed in the UL-MU transmission retriesthe data transmission using the existing backoff counter for asingle-user transmission as in the embodiment of FIG. 8, the STA mayhave two or more transmission opportunities through one contention forthe same data. In this case, the fairness of the channel access betweena STA participating in the UL-MU transmission and a STA notparticipating in the UL-MU transmission is lost.

Therefore, according to another embodiment of the present invention, aSTA which has failed in a UL-MU transmission regards that a single-usertransmission has failed and performs the subsequent channel accessprocedure. For this purpose, the STA participating in the UL-MUtransmission may decrement the backoff counter maintained by thecorresponding STA to 0. If the UL-MU transmission has failed, the STAincrements the retry counter for the corresponding access category by 1and obtains a new backoff counter within a range of a contention windowbased on the incremented retry counter. Upon the increment of the retrycounter, the contention window of the STA may change from the firstcontention window to the second contention window. If the size of thefirst contention window is not the maximum size of the contentionwindow, the size of the second contention window may be twice the sizeof the first contention window plus 1. The STA obtains a new backoffcounter within the second contention window and performs channel accessusing the obtained new backoff counter.

Referring to FIG. 9, the size of the first contention window of STA1 is15, and channel access is performed using a backoff counter 7 obtainedwithin the first contention window. In the first backoff procedure, thebackoff counter of STA1 is decremented to 3, and an UL-MU transmissionprocess by the trigger frame is started. STA1 participating in the UL-MUtransmission process may decrement the backoff counter to 0 and attempttransmission of the trigger-based PPDU. However, the UL-MU transmissionof STA1 has failed, and STA1 retries transmission of the correspondingdata through a single-user transmission. STA1 increments the retrycounter for the corresponding access category by 1 and obtains a newbackoff counter 13 within the size 32 of the second contention windowbased on the incremented retry counter. STA1 performs channel accessusing the obtained new backoff counter 13.

On the other hand, when carrier sensing is required before transmissionof the trigger-based PPDU, the channel may be determined to be busy as aresult of the carrier sensing so that the STA may not transmit thetrigger-based PPDU. According to a further embodiment of the presentinvention, if the channel is determined to be busy as a result of thecarrier sensing so that the trigger-based PPDU is not transmitted, theUL-MU transmission of the STA may not be regarded as failed. Thus, theSTA may not increment the retry counter for a single-user transmission.

FIG. 10 illustrates yet another embodiment of a subsequent operation ofthe uplink transmission terminal when the uplink multi-user transmissionhas failed. When participating in the UL-MU transmission correspondingto the trigger frame received from the AP, the STA should attempt totransmit data at an unintended point in time. Therefore, according toanother yet embodiment of the present invention, it is possible toreduce the penalty due to the UL-MU transmission failure. Morespecifically, if the UL-MU transmission has failed, the STA obtains anew backoff counter within the existing contention window range withoutincrementing the retry counter. The STA performs channel access usingthe obtained new backoff counter.

Referring to FIG. 10, the size of the initial contention window of STA1is 15, and channel access is performed using a backoff counter 7obtained within the initial contention window. In the first backoffprocedure, the backoff counter of STA1 is decremented to 3, and an UL-MUtransmission process by the trigger frame is started. STA1 participatingin the UL-MU transmission process may decrement the backoff counter to 0and attempt transmission of the trigger-based PPDU. However, the UL-MUtransmission of STA1 has failed, and STA1 retries transmission of thecorresponding data through a single-user transmission. STA1 obtains anew backoff counter 8 within the size 15 of the existing contentionwindow. STA1 performs channel access using the obtained new backoffcounter 8.

Uplink Multi-User Random Access

In the non-legacy wireless LAN system, UL-MU random access can beperformed. In an embodiment of the present invention, the UL-MU randomaccess may be performed through UL OFDMA-based random access. However,the present invention is not limited thereto. When the trigger frametransmitted by the AP indicates resource unit(s) allocated for randomaccess, STAs may perform random access via the corresponding resourceunit(s). A resource unit for random access (i.e., a random resourceunit) may be identified through a predetermined AID value. If an AIDsubfield of a user information field in the trigger frame indicates thepredetermined AID value, the corresponding resource unit may beidentified as a random resource unit. STAs may select at least one ofthe random resource unit(s) indicated through the trigger frame andattempt the UL-MU transmission via the selected random resource unit.

STAs attempting UL OFDMA-based random access perform contention toobtain transmission opportunity. A separate OFDMA backoff (OBO) counteris used for contention in the UL OFDMA-based random access. The OBOcounter is obtained within a range of an OFDMA contention window (OCW)managed for each STA. The AP transmits a minimum value of OCW (i.e.,OCWmin) and a maximum value of OCW (i.e., OCWmax) for OCW determinationof each STA through a random access parameter set. The random accessparameter set may be transmitted by being contained in at least one of abeacon, a probe response, a (re)association response, and anauthentication response. A STA that initially attempts the ULOFDMA-based random access sets the OCW of the corresponding STA to‘OCWmin-1’ based on the received random access parameter set. Next, theSTA selects an arbitrary integer within the range from 0 to OCW toobtain the OBO counter. In an embodiment of the present invention, theOBO counter and the OCW may represent a backoff counter for the UL-MUrandom access and a contention window for the UL-MU random access,respectively.

STAs decrement their OBO counter by the number of resource unit(s) onwhich random access can be performed each time a trigger frame istransmitted. That is, when N resource units(s) are allocated to therandom access, the STAs may decrement the OBO counter by a maximum of Nin the random access contention of the UL-MU transmission process by thecorresponding trigger frame. According to an embodiment of the presentinvention, the STA may decrement the OBO counter if the STA has pendingdata to be transmitted to the AP. If the OBO counter of the STA is lessthan or equal to the number of resource units(s) on which random accesscan be performed, the OBO counter of the STA is decremented to zero. Ifthe OBO counter is zero or decremented to zero, the STA may randomlyselect at least one of resource units(s) allocated for random access andperform an UL-MU transmission via the selected resource unit. A STA thathas failed to decrement the OBO counter to 0 in the correspondingcontention process may attempt random access by repeating theabove-described OBO counter decrementing process when the next triggerframe is transmitted.

FIG. 11 illustrates an embodiment of a UL OFDMA-based random accessprocedure. Each STA uses the OBO counter to contend for UL OFDMA-basedrandom access. In the embodiment of FIG. 11, a trigger frame 312indicates four random resource units. STAs receiving the trigger frame312 decrements an OBO counter of the corresponding STA based on thenumber 4 of the random resource units. In this case, OBO counters ofSTA1, STA2 and STA4 having an OBO counter less than or equal to thenumber 4 of the random resource units are decremented to 0. Thus, STA1,STA2 and STA4 can select one of the random resource units assigned bythe trigger frame 312 to transmit a trigger-based PPDU.

In the embodiment of FIG. 11, STA1 and STA4 select the same randomresource unit to transmit the trigger-based PPDU, which causes acollision. Therefore, STA1 and STA4 do not receive a responsecorresponding to the transmitted trigger-based PPDU. If the ULOFDMA-based random access has failed, the STA increments the OCW by apredetermined ratio and randomly obtains a new OBO counter within theincremented OCW range. Upon the increment of the OCW, the OCW of the STAmay change from the first OCW to the second OCW. If the size of thefirst OCW is not the maximum value of OCW, the size of the second OCWmay be twice the size of the first OCW plus 1. However, if the size ofthe existing OCW of the STA is equal to the maximum value of OCW, theSTA does not increment the OCW even if the random access has failed.That is, if the size of the first OCW is equal to the maximum value ofOCW, the second OCW may be set equal to the first OCW. In the embodimentof FIG. 11, STA1 and STA4 may randomly obtain a new OBO counter withinthe incremented second OCW, respectively, and participate in thesubsequent UL OFDMA-based random access procedure using the obtained newOBO counter.

FIGS. 12 to 15 illustrate embodiments of a UL OFDMA-based random accessprocedure when a carrier sensing is required before the transmission ofa trigger-based PPDU. In the embodiment of each drawing, duplicativedescriptions of parts which are the same or corresponding to theembodiments of the previous drawings will be omitted.

FIG. 12 illustrates the first embodiment of a UL OFDMA-based randomaccess procedure when a carrier sensing is required before thetransmission of a trigger-based PPDU. When a carrier sensing is requiredbefore the transmission of the trigger-based PPDU 422, 522, STAs shouldperform carrier sensing on the channel to be accessed. Trigger frames412 and 512 may indicate through a separate ‘CS required’ field whetheror not carrier sensing is required before the transmission oftrigger-based PPDUs 422 and 522. In this case, the carrier sensing maybe performed during a SIFS time between the trigger frames 412, 512 andthe trigger-based PPDUs 422, 522 transmitted in response thereto.

As described above, STAs whose OBO counter is 0 or decremented to 0 canselect one of the random resource units to attempt random access. Inthis case, the STA performs carrier sensing of the channel containingthe selected resource unit. If the channel containing the selectedresource unit is determined to be idle as a result of the carriersensing, the STA may transmit a trigger-based PPDU through the selectedresource unit. However, if the channel containing the selected resourceunit is determined to be busy as a result of the carrier sensing, theSTA cannot transmit the trigger-based PPDU through the selected resourceunit. If the trigger-based PPDU is not transmitted since the channel isdetermined to be busy as a result of the carrier sensing, the OCW andthe OBO counter for the STA to participate in the subsequent ULOFDMA-based random access procedure should be determined.

According to the first embodiment of the present invention, when thetrigger-based PPDU is not transmitted since the channel is determined tobe busy as a result of the carrier sensing, the STA may participate inthe subsequent UL OFDMA-based random access procedure while maintainingthe OBO counter at that point of time. That is, the STA maintains theOBO counter as 0 to participate in the subsequent UL OFDMA-based randomaccess procedure. If a carrier sensing is also required before thetransmission of the trigger-based PPDU in the subsequent UL OFDMA-basedrandom access procedure, the STA may transmit the trigger-based PPDUwhen the channel containing the selected resource unit is determined tobe idle.

Referring to FIG. 12, the first trigger frame 412 indicates 5 randomresource units and set the ‘CS required’ field to 1 to require carriersensing before the transmission of a trigger-based PPDU. STAs receivingthe first trigger frame 412 decrements an OBO counter of thecorresponding STA based on the number 5 of random resource units. Inthis case, OBO counters of STA1, STA2 and STA4 having an OBO counterless than or equal to the number 5 of random resource units aredecremented to 0. STA1, STA2 and STA4 perform carrier sensing forchannel access. The channel sensed by STA1 is determined to be idle, butthe channels sensed by STA2 and STA4 are determined to be busy. Thus,STA1 transmits a trigger-based PPDU 422 in response to the first triggerframe 412, but STA2 and STA4 do not perform random access. In this case,STA2 and STA4 may suspend the random access and participate in thesubsequent UL OFDMA-based random access procedure while maintaining theOBO counter 0.

In the embodiment of FIG. 12, the second trigger frame 512 indicates 5random resource units and sets the ‘CS required’ field to 1 to requirecarrier sensing before the transmission of the trigger-based PPDU. STAsreceiving the second trigger frame 512 decrements an OBO counter of thecorresponding STA based on the number 5 of the random resource units. Inthis case, OBO counters of STA3, STA5 and STA7 having an OBO counterless than or equal to the number 5 of random resource units aredecremented to 0. Further, in the previous UL OFDMA-based random accessprocedure, the OBO counters of STA2 and STA4 in which the random accessis suspended are 0. Thus, STA2, STA4, STA3, STA5 and STA7 performcarrier sensing for channel access. The channels sensed by STA2 and STA7are determined to be idle, but the channels sensed by STA4, STA3 andSTA5 are determined to be busy. Thus, STA2 and STA7 transmit atrigger-based PPDU 522 in response to the second trigger frame 512, butSTA4, STA3 and STA5 do not perform random access.

FIG. 13 illustrates the second embodiment of a UL OFDMA-based randomaccess procedure when a carrier sensing is required before thetransmission of a trigger-based PPDU. In a consecutive UL OFDMA-basedrandom access procedure, when STAs having an OBO counter of 0 arestacked, the probability of collision of random access STAs in thelimited resource unit is increased. Therefore, according to the secondembodiment of the present invention, when the trigger-based PPDU is nottransmitted since the channel is determined to be busy as a result ofthe carrier sensing, the STA obtains a new OBO counter to participate inthe subsequent UL OFDMA-based random access procedure. Morespecifically, the STA randomly obtains a new OBO counter within theexisting OCW and participates in the subsequent UL OFDMA-based randomaccess procedure using the obtained new OBO counter. If the STA does notaccess the channel due to the carrier sensing result, it cannot beregarded as a transmission failure and does not affect the channel forrandom access. Therefore, the OCW for obtaining the new OBO counter mayhave the same size as the existing OCW.

Referring to FIG. 13, the first trigger frame 414 indicates 5 randomresource units and sets the ‘CS required’ field to 1 to require carriersensing before the transmission of a trigger-based PPDU. As in theembodiment of FIG. 12, among the STAs that have received the firsttrigger frame 414, STA1, STA2, and STA4 whose OBO counters aredecremented to 0 perform carrier sensing for channel access. The channelsensed by STA1 is determined to be idle, but the channels sensed by STA2and STA4 are determined to be busy. Thus, STA1 transmits a trigger-basedPPDU 424 in response to the first trigger frame 414, but STA2 and STA4do not perform random access. STA2 and STA4 may suspend random accessand obtain a new OBO counter to participate in the subsequent ULOFDMA-based random access procedure. In this case, new OBO counters ofSTA2 and STA4 may be obtained within the existing OCW of thecorresponding STA, respectively. In the embodiment of FIG. 13, STA2obtains a new OBO counter 7 and STA4 obtains a new OBO counter 5.

In the embodiment of FIG. 13, the second trigger frame 514 indicates 5random resource units and sets the ‘CS required’ field to 1 to requirecarrier sensing before the transmission of the trigger-based PPDU. Amongthe STAs that have received the second trigger frame 514, STA3, STA4,STA5 and STA7 whose OBO counters are decremented to 0 perform carriersensing for channel access. The channels sensed by STA3 and STA7 aredetermined to be idle, but the channels sensed by STA4 and STA5 aredetermined to be busy. Thus, STA3 and STA7 transmit a trigger-based PPDU524 in response to the second trigger frame 514, but STA4 and STA5 donot perform random access. Meanwhile, the new OBO counter 7 obtained bySTA2 is larger than the number 5 of the random resource units indicatedby the second trigger frame 514. Therefore, STA2 does not transmit thetrigger-based PPDU and may participate in the subsequent UL OFDMA-basedrandom access procedure using the remaining backoff counter 2.

FIG. 14 illustrates the third embodiment of a UL OFDMA-based randomaccess procedure when a carrier sensing is required before thetransmission of a trigger-based PPDU. As described above, in theconsecutive UL OFDMA-based random access procedure, when STAs having anOBO counter of 0 are stacked, the probability of collision of randomaccess STAs in the limited resource unit is increased. According to thethird embodiment of the present invention, when the trigger-based PPDUis not transmitted since the channel is determined to be busy as aresult of the carrier sensing, the UL OFDMA-based random access may beregarded as failed. Thus, the STA increments the OCW by a predeterminedratio and randomly obtains a new OBO counter within the incremented OCWrange. As in the above-described embodiment, the size of the incrementedOCW may be twice the size of the existing OCW plus 1. The STA randomlyobtains the new OBO counter within the incremented OCW range andparticipates in the subsequent UL OFDMA-based random access procedure.

Referring to FIG. 14, the transmission process of the first triggerframe 416 and the corresponding trigger-based PPDU 426 is as describedin the embodiments of FIGS. 12 and 13. STA2 and STA4, in which thechannel is determined to be busy as a result of the carrier sensing, donot perform random access. STA2 and STA4 may suspend random access andobtain a new OBO counter to participate in the subsequent UL OFDMA-basedrandom access procedure. In this case, new OBO counters of STA2 and STA4may be obtained within the incremented OCW of the corresponding STA,respectively. In the embodiment of FIG. 14, STA2 obtains a new OBOcounter 7 and STA4 obtains a new OBO counter 5. After STA2 and STA4respectively obtain a new OBO counter, the transmission process of thesecond trigger frame 516 and the corresponding trigger-based PPDU 526 isas described in the embodiment of FIG. 13.

FIG. 15 illustrates the fourth embodiment of a UL OFDMA-based randomaccess procedure when a carrier sensing is required before thetransmission of a trigger-based PPDU. According to the fourth embodimentof the present invention, when a carrier sensing is required before thetransmission of the trigger-based PPDU, the STA may determine whether todecrement the OBO counter according to a result of the carrier sensing.When the channel containing the selected resource unit is determined tobe idle as a result of the carrier sensing, the STA may perform the OBOcounter decrement process described above. However, when the channelcontaining the selected resource unit is determined to be busy as aresult of the carrier sensing, the STA may participate in the subsequentUL OFDMA-based random access procedure while maintaining the OBO counterwithout decrementing the OBO counter. Thus, it is possible to preventSTAs having an OBO counter of 0 being stacked in the consecutive ULOFDMA-based random access procedure.

Referring to FIG. 15, the first trigger frame 418 indicates 5 randomresource units and sets the ‘CS required’ field to 1 to require carriersensing before the transmission of a trigger-based PPDU. STAs receivingthe first trigger frame 418 perform carrier sensing before thetransmission of the trigger-based PPDU. The channels sensed by STA1,STA4 and STA5 are determined to be idle, but the channels sensed by STA2and STA3 are determined to be busy. Thus, STA1, STA4 and STA5 decrementan OBO counter in response to the first trigger frame 418, but STA2 andSTA3 do not decrement an OBO counter. In this case, STA2 and STA3 maysuspend the random access and participate in the subsequent ULOFDMA-based random access procedure while maintaining the correspondingOBO counter. Similarly, STAs receiving the second trigger frame 518perform carrier sensing before the transmission of the trigger-basedPPDU. STA3 and STA5, which have determined that the channel on which thecarrier sensing is performed is busy, do not decrement an OBO counter inresponse to the second trigger frame 518.

The AP may allocate multiple channels for random access. According to anembodiment of the present invention, the STAs may perform the carriersensing on all channels to determine whether to decrement the OBOcounter. However, according to another embodiment of the presentinvention, the STAs may perform the carrier sensing for each allocated20 MHz channel. In this case, the STAs may attempt random access only tothe random resource units contained in the channel determined to beidle. According to an embodiment of the present invention, the STA maydecrement the OBO counter based on the number of random resource unit(s)contained in the channel determined to be idle.

FIGS. 16 to 18 illustrate embodiments of an OBO counter managementmethod of a STA that has succeeded in a UL OFDMA-based random access.

As described above, the AP may transmit a random access parameter set tothe STAs through a beacon 600 or the like. The random access parameterset includes the minimum value of OCW and the maximum value of OCW fordetermining OCW of each STA, or information that can be used to derivethese values. STAs attempting UL OFDMA-based random access determine anOCW between the minimum value of OCW and the maximum value of OCW, andrandomly select an OBO counter within the OCW range. If the triggerframe 610, 620 transmitted by the AP indicates at least one randomresource unit (or if one or more user information fields having apredetermined AID value indicating random access are present), STAs mayattempt random access through at least one of the indicated randomresource unit(s).

If the UL OFDMA-based random access has failed, the STA increments theOCW and randomly obtains a new OBO counter within the incremented OCWrange. As in the above-described embodiments, the size of theincremented OCW may be twice the size of the existing OCW plus 1. TheSTA randomly obtains a new OBO counter within the incremented OCW rangeto participate in the subsequent UL OFDMA-based random access procedure.On the other hand, if the UL OFDMA-based random access is successful,the STA resets the OCW to the minimum value of OCW. In this case, a rulefor obtaining a new OBO counter is required by the STA that hassucceeded in the UL OFDMA-based random access.

First, according to the embodiment of FIG. 16, the STA succeeding the ULOFDMA-based random access may participate in the subsequent ULOFDMA-based random access procedure while maintaining the existing OBOcounter. That is, the STA maintains the OBO counter as 0 to participatein the subsequent UL OFDMA-based random access procedure. Referring toFIG. 16, the first trigger frame 610 indicates 4 random resource units,and the second trigger frame 620 indicates 2 random resource units. TheOBO counter of STA1 receiving the first trigger frame 610 is decrementedto 0, and STA1 succeeds in transmitting a trigger-based PPDU. STA1 thathas succeeded in the UL OFDMA-based random access resets the OCW to theminimum value of OCW and maintains the OBO counter as 0. Upon receivingthe second trigger frame 620, since the OBO counter of STA1 is 0, STA1can transmit a trigger-based PPDU again. Thus, if the OBO counter ismaintained as 0, the STA will continue to have random accessopportunities until the UL OFDMA-based random access fails.

FIG. 17 illustrates another embodiment of the present invention. A STAthat has succeeded in the UL OFDMA-based random access may obtain a newOBO counter based on the reset OCW. In this case, the size of the resetOCW may be equal to the minimum value of OCW. The STA participates inthe subsequent UL OFDMA-based random access procedure using the new OBOcounter. Referring to FIG. 17, the OBO counter of STA1 receiving thefirst trigger frame 610 is decremented to 0, and STA1 succeeds intransmitting a trigger-based PPDU. STA1 that has succeeded in the ULOFDMA-based random access resets the OCW to the minimum value of OCW andobtains a new OBO counter 5 within the reset OCW. STA1 participates inthe subsequent UL OFDMA-based random access procedure using the new OBOcounter 5. The OBO counter of STA1 is decremented to 3 when receivingthe second trigger frame 620, STA1 does not perform the random accesssince the OBO counter is not decremented to 0. STA1 participates in thesubsequent UL OFDMA-based random access procedure using the remainingOBO counter 3.

FIG. 18 illustrates yet another embodiment of the present invention. ASTA that has succeeded in the UL OFDMA-based random access may notparticipate in the random access until it receives a new random accessparameter set. In the embodiment of FIG. 18, STA1 that has succeeded inthe random access in response to the first trigger frame 610 does notperform additional UL OFDMA-based random access until the next beacon700 containing the random access parameter set is received. Therefore,STA1 does not perform a separate random access when the second triggerframe 620 is received. According to an embodiment, STA1 may not resetthe OCW and OBO counter until it receives a new random access parameterset.

FIG. 19 illustrates an embodiment of a UL OFDMA-based random accessprocedure when a STA does not have pending data to be transmitted. A STAindicated to transmit a trigger-based PPDU may not transmit data ortransmit one or more QoS Null frames if the STA has no pending uplinkdata. However, if the STA which has no pending uplink data transmits aQoS Null frame in the random access procedure, the probability ofcollision in the random resource unit is increased. Therefore, accordingto the embodiment of the present invention, the STA may participate inthe UL OFDMA-based random access procedure only when the STA has pendingdata to be transmitted to the AP. A STA which has no pending data to betransmitted do not transmit any data, including QoS Null frames, throughrandom access.

FIG. 20 illustrates another embodiment of a UL OFDMA-based random accessprocedure when a STA does not have pending data to be transmitted.According to another embodiment of the present invention, when a STAwith no data to be transmitted in the EDCA buffer receives a triggerframe indicating the random resource unit, whether to attempt the randomaccess may be determined according to the selection of the STA.

As shown in FIG. 20(a), STA1 participating in the random access totransmit information such as the buffer status report may perform theabove-described OBO counter decrement process. When the OBO counter isdecremented to 0, STA1 may arbitrarily select at least one of the randomresource unit(s) to transmit a QoS Null frame. STA1 that has succeededin the UL OFDMA-based random access may reset an OCW and obtain a newOBO counter.

However, as shown in FIG. 20(b), when STA1 does not even transmit a QoSnull frame, STA1 does not perform the OBO counter decrement process.That is, according to an embodiment of the present invention, the STAmay decrement the OBO counter only if it has pending data to betransmitted to the AP. Since STA1 does not participate in random access,it does not reset an OCW after the corresponding random accessprocedure. That is, STA1 participates in the subsequent UL OFDMA-basedrandom access procedure using existing OCW and OBO counter.

FIGS. 21 and 22 illustrate protection methods of the UL OFDMA-basedrandom access procedure. A multi-user RTS (MU-RTS) may be used forprotecting data transmission in a multi-user transmission process. TheMU-RTS may have a variant format of the trigger frame and may solicitsimultaneous CTS transmission of at least one recipient via a userinformation field. The recipients receiving the MU-RTS transmitsimultaneous CTS after a SIFS time. The simultaneous CTS transmitted bymultiple recipients has the same waveform. The neighboring terminalsreceiving the MU-RTS and/or the simultaneous CTS may set a networkallocation vector (NAV).

According to the embodiment of the present invention, the UL OFDMA-basedrandom access procedure can be protected through transmissions of theMU-RTS and the simultaneous CTS. However, in the random accessprocedure, it is not possible to determine in advance which STA willattempt random access for data transmission. If all of the STAsattempting random access transmit the simultaneous CTS, unnecessaryprotection may be performed up to the radio range of the STA that hasfailed in random access as well as the STA that has succeeded in therandom access. As a result, performance of the adjacent network may bedegraded. Therefore, a method for minimizing the number of STAstransmitting simultaneous CTSs among STAs performing random access isneeded.

FIG. 21 illustrates an embodiment of a method for protecting the ULOFDMA-based random access procedure. According to an embodiment of thepresent invention, the AP may insert information on the number of randomresource unit(s) to be used in the UL OFDMA-based random accessprocedure into the MU-RTS and transmit it. The STA attempting randomaccess extracts the information on the number of random resource unitsfrom the received MU-RTS. The STA determines whether or not an OBOcounter of the STA can be decremented to 0 in the subsequent ULOFDMA-based random access procedure by referring to the extractedinformation on the number of random resource units. If the OBO countercan be decremented to 0, the STA transmits a simultaneous CTS. However,if the OBO counter cannot be decremented to 0, the STA does not transmita simultaneous CTS.

Referring to FIG. 21, the number of random resource units to be used inthe UL OFMDA-based random access procedure is 4. The AP transmitsinformation on the number of random resource units through an MU-RTS.STAs receiving the MU-RTS obtain the information on the number of randomresource units, and determine whether an OBO counter of thecorresponding STA can be decremented to 0 by referring to the obtainedinformation. In this case, STA1, STA2 and STA3 having an OBO counterless than or equal to the number 4 of random resource unitssimultaneously transmit simultaneous CTSs. However, STA4 and STA5 havingan OBO counter larger than the number 4 of random resource units do nottransmit simultaneous CTSs because they cannot decrement the OBO counterto 0 in the subsequent UL OFDMA-based random access procedure.

According to the embodiment of the present invention, the MU-RTS mayrepresent the information on the number of random resource unit(s) to beused in the subsequent UL OFDMA-based random access procedure in variousmethods. According to an embodiment, the MU-RTS may represent anidentifier separately designated for random access through an AID fieldor a ‘type-dependent per user info’ field, and may repeat it as many asthe number of random resource units(s). According to another embodiment,the MU-RTS may represent an identifier separately designated for randomaccess through the AID field and information on the number of randomresource unit(s) through the ‘type-dependent per user info’ field.According to yet another embodiment of the present invention, anidentifier representative of the number of random resource units(s) maybe specified and inserted into an AID field of a ‘per user info’ fieldof the MU-RTS. According to still another embodiment of the presentinvention, the MU-RTS may include a separate identifier for indicatingrandom access, and may represent information on the number of randomresource unit(s) through a specific resource unit pattern in a resourceunit allocation field.

FIG. 22 illustrates another embodiment of a method for protecting the ULOFDMA-based random access procedure. When a plurality of UL-MUtransmissions are performed in the same TXOP, the transmission andreception of MU-RTS and CTS for the target STAs in the entire UL-MUtransmission process can be performed at a start of the TXOP. In thiscase, the AP may insert information on the total number of randomresource unit(s) to be used in the UL OFDMA-based random accessprocedures to be protected into the MU-RTS and transmit it. The MU-RTSmay represent information on the total number of random resource unit(s)to be used in subsequent UL OFDMA-based random access procedures,through at least one of the methods described in the embodiment of FIG.21.

Referring to FIG. 22, two UL OFMDA-based random access procedures areperformed in the same TXOP, and the total number of random resourceunits to be used in these processes is nine. The AP transmits the totalnumber of random resource units via the MU-RTS. STAs receiving theMU-RTS obtain the information on the total number of random resourceunits and determine whether an OBO counter of the corresponding STA canbe decremented to 0 by referring to the obtained information. STA1 toSTA5 all have an OBO counter less than or equal to 9, so that the STAsmay transmit simultaneous CTSs.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

The invention claimed is:
 1. A wireless communication terminal, theterminal comprising: a processor; and a communication unit, wherein theprocessor is configured to: select an orthogonal frequency divisionmultiple access (OFDMA) random access backoff (OBO) counter within arange of a contention window, and receive a trigger frame includingresource allocation information, select a resource unit among one ormore resource units allocated based on the resource allocationinformation, and perform carrier sensing on a channel containing theselected resource unit when a specific field included in the triggerframe indicates performing the carrier sensing, wherein the OBO counteris decremented by a number of the one or more resource units, andwherein the OBO counter is set to ‘0’ when a value of the OBO counter issmaller than a number of the one or more resource units.
 2. The wirelesscommunication terminal of claim 1, wherein the processor is furtherconfigured to: receive contention window information related to thecontention window for performing an uplink OFDMA-based random access(UORA) of the terminal, wherein the contention window informationincludes a minimum value of the contention window, and wherein thecontention window is configured based on the minimum value.
 3. Thewireless communication terminal of claim 1, wherein an initial value ofthe contention window is set to the minimum value.
 4. The wirelesscommunication terminal of claim 1, wherein a new OBO counter isdetermined within the range of the contention window before a nexttrigger frame is received when the channel including the selectedresource unit for uplink multi-user transmission in response to thetrigger frame among the one or more resource units is busy according tothe carrier sensing and the OBO counter is 0 or decreased to
 0. 5. Thewireless communication terminal of claim 4, wherein the processor isfurther configured to: participate in a subsequent UORA using the newOBO counter, wherein the uplink multi-user transmission does not performthrough the selected resource unit when the channel is determined to bebusy based on the carrier sensing, and wherein the new OBO counter israndomly determined within the range of the contention window.
 6. Thewireless communication terminal of claim 5, wherein the contentionwindow for determining the new OBO counter has the same size as anexisting contention window.
 7. The wireless communication terminal ofclaim 1, wherein the uplink multi-user transmission is performed basedon the selected resource unit when the channel including the selectedresource unit is idle according to the carrier sensing and the OBOcounter is 0 or decremented to
 0. 8. The wireless communication terminalof claim 1, wherein the carrier sensing is performed during a SIFS timebetween the trigger frame and a PHY protocol data unit (PPDU)transmitted in response to the trigger frame.
 9. The wirelesscommunication terminal of claim 1, wherein the OBO counter does notdecrement when the trigger frame is received but there is no pendingdata to be transmitted to a base wireless communication terminal, andwherein a minimum value of the contention window is transmitted througha random access parameter set.
 10. A wireless communication method of awireless communication terminal, the method comprising: selecting anOFDMA OBO counter within a range of a contention window; and receiving atrigger frame including resource allocation information; selecting aresource unit among one or more resource units allocated based on theresource allocation information; and performing carrier sensing on achannel containing the selected resource unit when a specific fieldincluded in the trigger frame indicates performing the carrier sensing,wherein the OBO counter is decremented by a number of the one or moreresource units, and wherein the OBO counter is set to ‘0’ when a valueof the OBO counter is smaller than a number of the one or more resourceunits.
 11. The wireless communication method of claim 10, the methodfurther comprising: receiving contention window information related tothe contention window for performing an UORA of the terminal, whereinthe contention window information includes a minimum value of thecontention window, and wherein the contention window is configured basedon the minimum value.
 12. The wireless communication method of claim 11,wherein an initial value of the contention window is set to the minimumvalue.
 13. The wireless communication method of claim 10, wherein a newOBO counter is determined within the range of the contention windowbefore a next trigger frame is received when the channel including theselected resource unit for uplink multi-user transmission in response tothe trigger frame among the one or more resource units is busy accordingto the carrier sensing and the OBO counter is 0 or decreased to
 0. 14.The wireless communication method of claim 13, the method furthercomprising: participating in a subsequent UORA using the new OBOcounter, wherein the uplink multi-user transmission does not performedthrough the selected resource unit when the channel is determined to bebusy based on the carrier sensing, and wherein the new OBO counter israndomly determined within the range of the contention window.
 15. Thewireless communication method of claim 14, wherein the contention windowfor determining the new OBO counter has the same size as an existingcontention window.
 16. The wireless communication method of claim 10,wherein the uplink multi-user transmission is performed based on theselected resource unit when the channel including the selected resourceunit is idle according to the carrier sensing and the OBO counter is 0or decremented to
 0. 17. The wireless communication method of claim 10,wherein the carrier sensing is performed during a SIFS time between thetrigger frame and a PHY protocol data unit (PPDU) transmitted inresponse to the trigger frame.
 18. The wireless communication method ofclaim 10, wherein the OBO counter does not decrement when the triggerframe is received but there is no pending data to be transmitted to abase wireless communication terminal, and wherein a minimum value of thecontention window is transmitted through a random access parameter set.